Implement time:* 2.0.0 & 3.0.0 commands (#735)

* Finish ISteadyClock implementation

* Implement IsStandardNetworkSystemClockAccuracySufficient

Also use signed values for offsets and TimeSpanType

* Address comments

* Fix one missing nit and improve one comment

Ryujinx.HLE/HOS/Services/Bpc/IRtcManager.cs

@@ -0,0 +1,34 @@
+using System;
+
+namespace Ryujinx.HLE.HOS.Services.Bpc
+{
+    [Service("bpc:r")]
+    class IRtcManager : IpcService
+    {
+        public IRtcManager(ServiceCtx context) { }
+
+        [Command(0)]
+        // GetRtcTime() -> u64
+        public ResultCode GetRtcTime(ServiceCtx context)
+        {
+            ResultCode result = GetExternalRtcValue(out ulong rtcValue);
+
+            if (result == ResultCode.Success)
+            {
+                context.ResponseData.Write(rtcValue);
+            }
+
+            return result;
+        }
+
+        public static ResultCode GetExternalRtcValue(out ulong rtcValue)
+        {
+            // TODO: emulate MAX77620/MAX77812 RTC
+            DateTime unixEpoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+
+            rtcValue = (ulong)(DateTime.Now.ToUniversalTime() - unixEpoch).TotalSeconds;
+
+            return ResultCode.Success;
+        }
+    }
+}